This invention relates generally to hypodermic syringes, and more particularly to pre-filled syringes of the type employing a needle which can be installed on and removed from the syringe barrel whereby needles of varying lengths and different characteristics can be used with existing syringe structures. In the past various needle retainer and locking devices have been proposed and produced. One type employed a turnable locking member carried on the syringe barrel, the member having a sharp cutting retainer edge which was adapted to bite into the relatively softer needle hub after the latter was inserted into the barrel and the member turned. Other constructions involving chuck-type syringes employed a slotted sleeve which was carried on the needle and which could be engaged by the jaws of a chuck after the needle was inserted and the chuck tightened. Still another arrangement incorporated a threaded socket carried by a syringe which received a similarly threaded nozzle portion of the needle hub, whereby the needle pierced a sealing membrane as the nozzle was threaded into the socket.
The above constructions had a number of distinct drawbacks and disadvantages. The constructions employing mating screw threads were rather expensive to produce and manufacture, due to the close tolerances required to insure smooth operation of the co-operable threads. In prior devices where the hub and needle were free to turn as the latter pierced a sealing membrane, there was the danger that minute pieces of the membrane would be torn off by the needle point as it rotated. These pieces were sometimes drawn into the hollow needle and injected into a patient with serious consequences. In addition, where threaded parts were involved there was always the danger that during assembly or use the threads might not be "started" properly, thus resulting in binding or damage and malfunction.